The purpose of this study is to determine the appropriate dose of an investigational drug, called PS-341, in human patients. This drug works by blocking the function of some the of the proteins in cells that are responsible for making them divide (it falls into the class of drugs known as "proteasome inhibitors"). Based on results from laboratory studies using this drug in animals, there is some evidence that this drug may be able to help control hematologic malignancies (such as Leukemia, Lymphoma, Myeloma, and Hodgkin's disease) in people.